Gulf 'dead zone' bigger than average but not a record

Jul. 29, 2013
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The 2013 dead zone is located off the Louisiana coast in the Gulf of Mexico. / LUMCOM

by USA TODAY

by USA TODAY

NEW ORLEANS (AP) - This summer's "dead zone" at the bottom of the Gulf of Mexico, where there's so little oxygen that starfish suffocate, is bigger than average but doesn't approach record size as scientists had predicted, according to findings released Monday.

The area of low oxygen covers 5,840 square miles of the Gulf floor - roughly the size of Connecticut, said scientists led by Nancy Rabalais of the Louisiana Universities Marine Consortium. The National Oceanic and Atmospheric Administration (NOAA) has been paying for studies of the dead zone since 1985.

Rabalais said the survey boat encountered some bottom-dwelling eels and crabs that had swum near the surface of water that's 60 to 70 feet deep to find oxygen.

"That's a long way for something like an eel, that lives buried in the mud, to find its way to the surface," she said in an interview.

The low oxygen kills animals that cannot swim away, such as worms, starfish, small burrowing shrimp and some crabs, hurting food quality for fish that return in the fall when oxygen levels rise, she wrote in her annual report.

The dead zone is caused when nitrogen and phosphorus, much of it from farm fertilizer in the 41-state Mississippi River basin, feed algae blooms at the river's mouth. Algae and the protozoa that eat them die and fall to the bottom, where their decomposition uses up oxygen.

Scientists from Louisiana State University and the University of Michigan had expected a wet spring to bring more nutrients than usual down the Mississippi River, leading to a dead zone that could have approached or exceeded the largest-ever. The largest dead zone on record was in 2002, when it spread across 8,481 square miles of the Gulf.

Data indicates that high winds in early to mid-July mixed oxygen into deeper waters, Rabalais said. Other winds pushed the zone's western edge farther east than usual, she said.

The dead zone has averaged 5,176 square miles over the past five years. The smallest dead zones were 15 square miles in 1988 and 1,696 in 2000.

The Mississippi River Collaborative, a partnership of environmental organizations and legal centers in states along the Mississippi River, sued the U.S. Environmental Protection Agency last year, calling for it to set standards for nitrogen and phosphorus pollution and make states meet them.

Both sides have submitted legal briefs; U.S. District Judge Jay Zainey has not indicated whether he will schedule oral arguments.

"EPA told states to develop numeric nitrogen and phosphorus limits 15 years ago," Cynthia Sarthou, executive director for the Gulf Restoration Network, a coalition member, said in a news release. "EPA has spent the decade and a half since backing off hard deadline after hard deadline for reducing dead zone-causing pollution."

The fertilizer chemicals are creating problems further north.

From May through most of July, nitrate levels spiked in the two rivers that provide drinking water to about 500,000 people in the Des Moines area. Des Moines Water Works had to use its nitrate removal facility and alternate water sources and ask customers to cut water use until about July 24. The total cost was $525,000, officials said.

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